1. Field of the Invention
This invention relates to power supplies and, more particularly, to power supplies having fault responsive means to protect the system from the consequences of a fault condition and indicator means for isolating the fault.
2. Brief Description of the Prior Art
When complex power supply systems which supply a number of different A.C. and D.C. voltage levels to a plurality of loads, such as are required by printers used as peripherals to computer systems, develope a fault condition (for example, an undervoltage, overvoltage or overcurrent condition in one of the subcircuits of the system), means are usually provided to protect the system, for example, by cutting off the A.C. power line to the system. It is then a difficult and time consuming task for a service technician in the field to locate the site and cause of the problem so that he may replace the field replaceable unit in which the problem resides.
Although there are a number of suggestions in the prior art of systems having means to indicate the location of faults or other conditions, none of these relate to isolating faults in complex power supply systems. In British Pat. No. 2,036,390, for example, each fault in a data processing system, such as a centrally controlled telephone exchange, sets a "1" bit into a shift register at a position appropriate to the faulty device's identity. When a central processor needs a fault report, it clocks a counter while sifting the register so that the bits appear at the rightmost stage. The processor samples each bit to decide if it is a "1". If not, another clock pulse implements the count, while the shift register shifts another bit to the rightmost edge. The process repeats until "1" is found. The count residing in the counter indicates which data processing system has failed.
U.S. Pat. No. 4,521,885 discloses a diagnostic display apparatus for an electro-mechanical system, such as, an electrical vehicle or lift truck, which senses and displays the condition of electro-mechanical components prior to and during machine operation. Sensors are mounted on the accelerator pedal and steering wheel to generate BCD signals representing the pedal position and steering wheel angle. Sensors also monitor operator panel switches which control the forward and reverse movement direction of the vehicle and a battery level detector showing the charge remaining on the vehicle battery. A software programmable processor generates a series of command signals guiding the serviceman in forming a series of tests. A diagnostic code is displayed when a faulty element is found.
U.S. Pat. No. 4,062,061 discloses a copying machine under the control of a CPU module. If an electro-mechanical component of the machine experiences some nature of operational difficulty, a fault flag is set in an error log. Display means visually identifies the fault location, and a permanent record is stored in memory for future use by a service technician.
U.S. Pat. No. 4,039,813 relates to apparatus and a method for diagnosing digital data devices. A counter is used to address an array in conjunction with bits set into a select register. The location of the array address indicates a section of a logical system selected to be tested. A large logic system may now be partitioned into smaller sections and a pre-programmed test may be applied to the individual sections for narrowing down a failure. The counter keeps track of which section of the logic system is under test so that the expected results from the test may be compared for accuracy.
Although these prior art devices are useful for isolating faults, they donot associate the fault isolation with means to shutdown the system for preventing further damage. None of these prior art systems isolate faults in a power supply system, and the fault isolation means used, employing shift registers and programmed processors, are relatively complex and expensive.